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By jepito - 14 Years Ago
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Machine shop called to tell me my 312 block has a sizable crack in the water jacket. I just pulled the engine out of my 56 merc parts car to find it has a 292. This will be a high performance build and crank offset ground to increase stroke. Now the question, am I better off cutting the crank down to 292, or align boring the block to the larger main size? I'm more concerned with doing it the best way rather than the cheap way.
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By fairlane bob - 14 Years Ago
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I believe you find it's a better idea to turn the 312 crank mains down to 292 size ,bearings and the rear seal are easier to git and block is stronger . Make sure the machine shop turns the rear seal area correctly.
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By aussiebill - 14 Years Ago
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fairlane bob (10/31/2011)
I believe you find it's a better idea to turn the 312 crank mains down to 292 size ,bearings and the rear seal are easier to git and block is stronger . Make sure the machine shop turns the rear seal area correctly.Make sure also they turn the oil slinger down to 292 crank size also.
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By Hoosier Hurricane - 14 Years Ago
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I'm in the minority here, but I prefer to bore the block to 312 main size. That way I don't reduce the overlap between the throws and the main journals on the crank. I don't bore the rear seal area, and turn the 312 crank's seal area to 292 size, and use 292 neoprene seals. Which ever you choose, if the crank gets reground, make sure the machinist dresses a radius on his grinding wheel so that the original radii on the journals remain. The two cranks that I have broken were regrinds with the radius gone. The cracks started in the areas where the radii used to be.
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By fairlane bob - 14 Years Ago
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John Thats one of the reasons I said about turning the crank down I kinda remember us talking about turning the cranks and you talking about trouble gitting shops to dress the grinding wheel to properly radius the crank throw,and what I've seen the main bearing and seals seem to be cheaper for 292's than 312's
HOP
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By jepito - 14 Years Ago
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The overlap was my concern with the offset grind and smaller mains. Has any one had a crank fail that was properly ground?
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By Hoosier Hurricane - 14 Years Ago
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I have not had one break, but I have found a couple with cracks forming in the radii after 3-4 seasons of drag racing in my supercharged 312s. I finally adapted a fluid damper and the cracking hasn't shown up yet.
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By Ted - 14 Years Ago
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Total agreement with John about the journal radii. Regardless of which tack you take on using the 312 crankshaft, be sure that the radius is maintained at the journal edges. My own druthers for the cast 312 crankshaft is to cut the mains down to the 292 size as this allows the main bolt threads to be spaced further from the main bearing bore itself. Bearing speed is the other consideration as the 292 mains do free up some additional horsepower. On the flip side of all this is the overlap that John mentions but I’ve yet to have a problem with this to date when machining the cast cranks but journal filet radii is part of the equation here. The other part of the equation is how finely the crankshaft and the related components are balanced. As John mentions, there are some differing opinions on this and this one’s mine.
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By mctim64 - 14 Years Ago
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I too prefer to make the crank fit the block. I am very adamant about the radius though, I don't know how many times I've had to tell someone their crank is junk because a crack has started in a fillit with no radius. I was fortunate to learn a long time ago how important the radius is, the first shop I worked for just wanted you to dress the edge of the grinding stone with a diamond "free hand" this was quick but not good enough.
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By hjh - 14 Years Ago
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Jepito What is your location? I`m in south west Ohio . I should have what you need , either a 312 block or C2AE ''292'' or other. If interested give me a call if no answer leave message & I will call back. Thanks Harry Hutten 513-868-3311
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By pegleg - 14 Years Ago
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Some time back the factories used to roll the radius and undercut it. That's a fairly labor intensive operation or time consuming, depending on how it was done. the fact that they thought it was necessary should tell us how important they thought it was. As I remember Pontiac did this on some of the Ram Air motors which used cast iron (not steel) cranks. Actually they were nodular iron. Guys who didn't duplicate that feature on rebuilds wound up with rotating parts in the oil pan. Those cranks had relatively huge mains and large rods, a lot of journal overlap.
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By GREENBIRD56 - 14 Years Ago
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Are there any drawings, sketches or machining diagrams available that show the crankshaft details we are discussing? I have found a what my partner in crime says is a decent 312 crank (has the right main journal size and no wounds anyway) - and I'm headed over to get it Friday afternoon. The business of the corner radii - and their impact on fatigue life has to be seen to be believed. It can drastically alter the life of a part - alonng with nicks and scratches you'd never suspect. So the whole thing will get a close going over before I get too carried away....... The details of the tail end oil seal and slinger of the 292 are not familiar to me. I may have to just hunt down a junker to have a better look - but drawings would be a help.
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By grovedawg - 14 Years Ago
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Do what you think is best (both work well) and in the end you'll be happy.
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By NoShortcuts - 14 Years Ago
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GREENBIRD56 (11/8/2011)
Are there any drawings, sketches or machining diagrams available that show the crankshaft details we are discussing? The details of the tail end oil seal and slinger of the 292 are not familiar to me. I may have to just hunt down a junker to have a better look - but drawings would be a help.
Google 'john mummert y-block' or 'ford y-block.com'. Toggle the subheading 'Technical'. From the list of technical topics that opens, toggle 'Crankshaft Identification'.
At the top of the page that opens is the crankshaft dimensional info. you are seeking.
Hope this helps.
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By pegleg - 14 Years Ago
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Steve, Call Mummert or Ted. Either guy will be able to sketch it for you.
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By John Mummert - 14 Years Ago
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I wouldn't be concerned about the reduction in journal overlap on the mains. You will only be reducing the O.D. of the main .125" so this makes the reduction 1/2 that or .062". You are offset grinding the rods to increase the stroke and will be reducing the overlap by either .085" if going to 2.100" journal or .185" if going to 2.00" journal because all of the material is removed from the overlap side of the rod journal.
If the radius is properly ground you will not have a problem. Radius needs to be between .090 and .125". Larger is better but more care must be taken with a larger radius. There is a greater chance of the rod bearing riding up on the radius and pinching off oil flow off the bearing. Bearings require oil flow, not just pressure. Use narrowed bearings and check carefully that the rod can move up to the crank cheek and the side of the bearing doesn't get too close to the radius.
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By GREENBIRD56 - 14 Years Ago
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Thanx John - that recommended corner radii was one of the basic things I was interested in.
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By pegleg - 14 Years Ago
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Hoosiers concern, and mine, is the front journal on the blower cars. The belt tension of the blower will fatigue the fillet after a while. No blower, no problem.
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